This invention relates to the termination of mineral insulated electric cables, that is to say cables of the kind comprising at least one conductor insulated from a surrounding metal sheath, and where there is more than one conductor from the other conductor or conductors, by compacted mineral insulating powder, usually but not necessarily magnesium oxide.
Compacted mineral insulating powder is particularly vulnerable to water penetration and it is the general practice to protect an end of a mineral insulated cable against the ingress of moisture by a metal sealing pot which is screwed or otherwise secured to the cable sheath and which is filled with waterproof sealing compound. Assembly of a sealing pot on an end of a mineral insulated electric cable in such a way as to provide an effective waterproof termination requires a degree of skill and the time taken to terminate mineral insulated electric cables of a mineral insulated electric cable installation contributes to a substantial proportion of the overall cost of the installation.
It has been proposed to provide a mineral insulated cable termination of a kind which can be readily assembled by semi-skilled or unskilled personnel. In one mineral insulated cable termination of this kind, the cut-back end of the cable is sealed by a preformed cap of electrically insulating material comprising a tube which over a part of its length extending from one of its ends effects a circumferentially continuous, substantially fluid-tight fit around the cable sheath and which at the other of its ends has an end wall integral with the tube and spaced from the end face of the cable, the end wall of the cap having a throughbore or throughbores through which the cable conductor or conductors passes or pass and the space within the cap between the end face of the cable and the end wall being filled with waterproof electrically insulating compound. With a view to reducing the risk that the cap can be inadvertently removed from the end of the cable, it has been proposed to employ in a termination of this kind a supplementary device which mechanically secures the cap to the cable sheath. This supplementary device may take the form of a collar of metal or metal alloy surrounding the cap which is radially inwardly distorted to clamp the cap to the cable sheath or which, over a part of its length, effects direct mechanical engagement with the cable sheath.
It is an object of the present invention to provide an improved form of mineral insulated cable termination which can be readily assembled and mechanically secured to the cable sheath by semi-skilled or unskilled personnel.